Method for completing wells

ABSTRACT

A method for completing a well whose wellbore passes through a permafrost zone wherein in at least part of the permafrost zone, concentric outer and inner casing strings are placed in the wellbore, the outer casing string having conductor means for establishing communication between the exterior of the outer casing and the annulus between the inside of the outer casing and the outside of the inner casing so that after placing cement in the various annuli around the various casing strings, the cement in the annulus between the outer and inner casing strings can be washed out utilizing the conductor means, and thereafter the wash fluid can be purged from said annulus by way of said conductor means using a gas. The purged annulus is then refilled with cement which has a carefully controlled water content so that this cement and its adjacent casing will not be subjected to stress due to freezing of substantial amounts of water. This invention also applies to a well casing shoe which has a cylindrical body adapted to fit on a section of casing, the body carrying a conductor means having an aperture therein for communicating between the interior and exterior of the body. The aperture can have a rupture means therein for preventing fluid such as drilling mud or cement from entering the conductor means before the washing step is to be carried out. This invention also applies to a well casing string composed of a plurality of casing sections, the casing string carrying a conductor means according to this invention for establishing communication between the interior and exterior of the string. For example, the casing string can carry a casing shoe which in turn carries a conductor means.

United States Patent Bell et al.

METHOD FOR COMPLETING WELLS Inventors: Larry N. Bell; Charles R.Knowles,

both of Anchorage, Alaska; Frank J. Schuh, Dallas, Tex.

[73] Assignee: Atlantic Richfield Company, Los

Angeles, Calif.

[22] Filed: Apr. 29, 1974 [2|] Appl. No.: 465,181

[52] US. Cl. 166/285; loo/DIG. 1 [5|] Int. Cl E2lb 33/14 [58] Field ofSearch 166/285, DIG. l, 292, 29]

[56] References Cited UNITED STATES PATENTS 3,0l3.608 l2/l96l Church166/285 X 3,l93.0l() 7/1965 Bielstein l66/285 3,373.8ll 3/1968 Burtch166/292 X 3.4l6,602 ill/1968 Boughton lob/292 3.502.l48 3/1970 Slagle etal.. l66/292 3.56l,53l 2/l97l Miller lob/285 3.84l.404 Ill/I974 Harmonlob/DIG. l X

Primary Examiner-Stephen J. Novosad Attorney, Agent, or FirmRoderick W.MacDonald [57] ABSTRACT A method for completing a well whose wellborepasses through a permafrost zone wherein in at least part of thepermafrost zone, concentric outer and inner casing strings are placed inthe wellbore, the outer casing string having conductor means forestablishing communication between the exterior of the outer casing andthe annulus between the inside of the outer casing and the outside ofthe inner casing so that after placing cement in the various annuliaround the various casing strings, the cement in the annulus between theouter and inner casing strings can be washed out utilizing the conductormeans, and thereafter the wash fluid can be purged from said annulus byway of said conductor means using a gas. The purged annulus is thenrefilled with cement which has a carefully controlled water content sothat this cement and its adjacent casing will not be subjected to stressdue to freezing of substantial amounts of water. This invention alsoapplies to a well casing shoe which has a cylindrical body adapted tofit on a section of casing, the body carrying a conductor means havingan aperture therein for communicating between the interior and exteriorof the body. The aperture can have a rupture means therein forpreventing fluid such as drilling mud or cement from entering theconductor means before the washing step is to be carried out. Thisinvention also applies to a well casing string composed of a pluralityof easing sections, the casing string carrying a conductor meansaccording to this invention for establishing communication between theinterior and exterior of the string. For example, the casing string cancarry a casing shoe which in turn carries a conductor means.

4 Claims, 3 Drawing Figures PATENTEU W 8 I975 sumznrg FIG. 3

FlG.2

FIG.3

METHOD FOR COMPLETING WELLS BACKGROUND OF THE INVENTION Heretofore, incompleting a well, such as an oil and- /or gas well, whether in or outof permafrost areas, various sizes and lengths of easing strings are setin the wellbore. The casing strings extend to various depths and are setconcentrically about one another in the wellbore. Thus, in a given well,there can be at least two casing strings, each casing string composed ofa plurality of individual sections of easing pipe. The casing stringsare concentrical with but spaced from one another to provide annularspaces therebetween. The inner or smaller diameter casing string extendsto a greater depth in the wellbore than the next larger diameter orouter casing string. Normally, the annuli between adjacent casingstrings and between a casing string and the wall of the wellbore arefilled with cement. The cement conventionally contains substantialamounts of water. In permafrost wells, care should be taken thatsubstantial amounts of liquid water from the drilling fluid and cementdo not remain in the permafrost zone because the water can freeze intosolid ice and cause undesirable pressure to build up in the well.

SUMMARY OF THE INVENTION It has been found that it is quite importantthat elevated pressures due to liquid water freezing be avoided in anannulus between two concentric strings of easing because damage to oneor both casing strings is more likely to occur in this annulus than inthe annulus between a casing string and the wall of the wellbore.

Thus, according to this invention, special precaution is taken to insurethat the cement disposed in an annulus between two casing strings has avery carefully controlled water content, i.e., a very low water content,and that there is essentially no residual drilling fluid present so thatthere is not sufficient water in the annulus to cause any damage to thecasing strings should that water freeze into solid ice.

The method according to this invention relates to the steps ofcompleting a well in the permafrost zone using at least one set of innerand outer concentric strings of easing, the inner string extending to adepth lower than the outer string, wherein the annulus caused by theoverlapping of the inner and outer strings of easing, after cementingall of the casing but before the cement hardens, is subjected to awashing step to wash the cement out of this annulus. The wash fluid isthereafter forcibly displaced from the annulus by a gas so that theannulus between the two casing strings is thoroughly purged. Thereafterthe purged annulus is filled with a cement composition which is verycarefully controlled as to its low water content.

This invention also employs apparatus which uses a conductor means forestablishing communication between the interior and exterior of theouter casing string so that the above-described washing and gas purgingsteps can be accomplished in the annulus where the inner and outercasing strings overlap. The conducting means can be carried on thecasing string or on a casing shoe on the casing string. The conductormeans preferably contains a rupture means which is intact when the outerand inner easing strings are set in the wellbore so that when the firstcementing step is carried out cement cannot enter the conductor means.

Thereafter, when it is desired to carry out the washing and gas purgingsteps, the rupture means is broken such as by pressuring up the washingfluid to establish communication between the interior and exterior ofthe outer casing string by way of the conductor means.

Accordingly, it is an object of this invention to provide a new andimproved method for completing wells in permafrost.

Other aspects, objects and advantages of this invention will be apparentto those skilled in the art from this disclosure and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cross section oftheelevation of a well completed in accordance with this invention.

FIG. 2 shows the cross section of the elevation of a well casing shoe inaccordance with this invention.

FIG. 3 shows a transverse cross section of the casing shoe of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 there is shownpermafrost l which extends from the earths surface 2 down to level 3below which is unfrozen ground 4. Wellbore 5 is composed of twosections, the upper section 6 being ofa larger cross sectional diameterthan the lower portion 7. Outer and inner casing strings 8 and 9,respectively, are placed concentric with one another within wellbore 5so that string 8 extends to the bottom 10 of wellbore portion 6 whileinner string 9 extends below the lower end of string 8 down into lowerportion 7 and even below the end of the permafrost at level 3. Thus,there is provided a first annulus which extends between the outersurface of outer string 8 and the wellbore wall of portion 6 asdesignated by arrow I2. A second annulus is provided between theinterior of easing 8 and the exterior of casing 9 as represented byarrow 13 and extends longitudinally the length of overlap betweencasings 8 and 9 in the permafrost as shown by bracket 14. A thirdannulus extends between the outside of string 9 and the wellbore wall ofportion 7 as shown by arrow 15 and also extends longitudinally from thebottom of second annulus 14 to the bottom I7 of easing string 9 as shownby bracket 16.

Casing string 8 carries at the bottom thereof conducting means 20 whichhas an aperture 21 therein. Conduit means 22 is connected to aperture 2Iand extends to the earths surface. A blowout preventer means for closingthe annulus between casings 8 and 9 is provided at 23, and pipe means 24and 25 are provided below and above, respectively, blowout preventer 23.Pipes 24 provide access to second annulus 13 even after blowoutpreventers 23 are closed. Annuli l2, l3, and 15 are shown in FIG. 1 tobe filled with cement from the bottom of the wellbore to the earth'ssurface.

In practicing the method of this invention, after emplacing theconcentric casing strings 8 and 9 with the outer casing string carryinga conductor means with a conduit means connected thereto as shown inFIG. I, and after placing cement in all three annuli as shown in FIG. I,but before the cement hardens, the cement in annulus I3 which is thecement between the two casing strings must be carefully treated toprevent leaving substantial amounts of liquid water in that annulus I3.

Conductor means 20 preferably has a rupture means or some other type ofbreakable plug in aperture 21 during the initial emplacement of cementin annuli l2.

l3. and 15. The rupture means is shown in more detail in FIG. 2hereinafter. The rupture means in aperture 21 prevents cement frompassing into conduit means 22. When the initial cementing step iscompleted and before the cement has hardened. it is then desirable tobreak the rupture means thereby establishing communication between theinterior. i.e.. annulus I3. and the exterior. i.e.. annulus 12, ofeasing string 8. Thus. communication is. in effect. established frompipes 24 andfor 25 to annulus 13 through casing string 8 by way ofconductor means 20, and to the earths surface by way of conduit means22.

A washing fluid such as liquid water or a hydrocarbon or other liquidreadily available at the drill site can then be employed to wash thestill fluid cement out of annulus I3 using conduit means 22 and therebyremoving substantially all material (cement, drilling fluid. etc.) fromannulus I3 and leaving behind primarily only wash fluid. The wash fluidcan be introduced by way of conduit means 22 and removed by way of pipes24 and/or 25, or introduced by pipes 24 and/or 25 and removed by way ofconduit means 22, or a combination thereof in any sequence of steps orrepetition of steps desired so long as the primary object of thedisplacement of substantially all of the material from annulus 13 bywash fluid is achieved.

Thereafter. the remaining wash fluid. which extends for the length 14 ofannulus l3 and fills conduit means 22. is forced or otherwise purgedfrom annulus l3 and conduit means 22 by pressurization with a gas suchas air or any other suitable gas for forcing substantially all thewashing fluid from the annulus and the conduit means. This leaves anessentially empty annulus I3 which can then be filled with a cementcomposition V which has a very carefully controlled water content. Thissecond cement composition can be a much more expensive cementcomposition than that used in the initial cementing step since all ithas to fill is annulus l3, annuli l2 and I5 already being filled with aless expensive cement composition. By following this method it is maderelatively certain that no water or drilling fluid contaminated cementis left between casing strings 8 and 9 in permafrost zone 1.

FIG. 2 shows a well casing shoe which can be used in the embodiment ofFIG. I. FIG. I shows conducting means to be carried by and at the bottomend of easing string 8. FIG. 2 shows a casing shoe having a rightcylindrical body 30 which has at its upper or first end 31 a threadedportion for ease of attachment to the lower end ofa casing string suchas casing string 8 and which also has at a lower point thereof such asthe bottom or second end 32 of body 30 conductor means with aperture 2].The conductor means 20 does not have to be at the very bottom of easing8 or body 30. The conductor means can be at an intermediate point alongcasing 8 or body 30. but is preferably in the lower half of casing 8whether it is carried by the casing or a casing shoe. Upper end 33 ofaperture 2] is threaded to receive a threaded end of conduit means 22 asshown in FIG. I. Aperture 2I contains therein an unbroken rupture means34, composed of graphite. or aluminum or any other suitable material. sothat fluid cannot pass through aperture 2] until rupture means 34 isbroken. The first and second ends of body are open so that fluid canpass from the interior of the casing string out through the bottom ofthe casing string and vice versa.

FIG. 3 shows body 30 of FIG. 2 to carry two conducting means 20 onopposite sides thereof. According to this invention one or more than twoconducting means can also be employed on the casing shoe or on theeasing itself as desired. The shoe of FIG. 2 does not have to be placedat the bottom end of easing string 8 but could be applied to anintermediate point thereof if desired, but it is preferable that theconductor means be at or near the bottom of easing string 8 so that themajority of annulus 13 is subjected to the washing and gas purgingstepsv Of course. a conventional wellhead can be employed at the earthssurface for easing strings 8 and/or 9 but is not shown for sake ofsimplicity. Also, wellbore portion 7 can extend below the level shown inFIG. 1 but normally. after all cementing steps are completed, thewellbore will then be drilled deeper by passing a drill bit and drillstring through the interior of casing 9 and drilling through the cementbelow end 17 of easing 9 and on into the unfrozen earth 4.

EXAMPLE In a situation where permafrost zone 1 extends to about 2.000feet below earths surface 2, 20 inch diameter casing string 8 is setabout eighty feet below the earth's surface. i.e.. at the bottom ofwellbore portion 6 while l3% inch diameter casing string 9 extends toabout 2.700 feet below the earths surface 2. Two-inch tubing is employedfor conduit means 22 and aperture 2I contains an aluminum rupture diskwhich has a burst pressure of about 200 psig. Annuli l2. l3, and 15 arecemented in a conventional manner which conventional cement normallyused in permafrost regionsv Before the cement in annulus 13 sets. wateris pumped down conduit means 22 at sufficient pressure to burst therupture means in the aperture 21 so that water rises from the bottom ofannulus 13 toward the earths surface pushing ahead of it and/or mixingand carrying with it the cement and any residual drilling fluid in thatcement and any other material present in annulus 13. This washed outmaterial is recovered at the earths surface by way of pipes 24 and/or25. Thereafter. blowout pre venter 23 is closed and water is pumped byway of pipes 24 into the top of annulus I3 down to the bot tom of thatannulus. through aperture 21. and up conduit means 22 to the earthssurface. After this reverse washing step. rig air is used to force thewater wash fluid remaining in annulus I3 and conduit means 22 to theearth's surface by injecting the air by way of pipes 24 into the top ofannulus l3 and forcing the water out of annulus 13 into conduit means 22and out of conduit means 22 to the earth's surface. Normally. abouteighty cubic feet per minute of air at about I50 psig can be employed toaccomplish the purging step. Thereafter. annulus I3 is recemented usingcement with essentially no free water. i.e.. using no more water than isrequired to hydrate the cement.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

I. A method for completing a well whose wellbore passes through apermafrost zone comprising. in at least a portion of said permafrostzone. placing in said wellbore a first casing means which carries nearthe lower end thereof a conductor means for passing fluid between theinside and outside of said first casing means, said conductor meansinitially having a rupture means for preventing the passage of fluidtherethrough, said first casing means being spaced from the wellborewall to provide a first annulus. conduit means extending in said firstannulus from said conductor means to the surface of the earth, placing asecond casing means inside said first casing means but spaced therefromto provide a second annulus between said first and second casing means.said second casing means extending below the lower end of said firstcasing means to provide a third annulus around that portion of saidsecond casing means which extends below said lower end of said firstcasing means, placing cement in said first. second and third annuli,before said cement hardens. breaking said rupture means. circulating awashing fluid through said second annulus-conductor meansconduit meansassembly to wash substantially all material out of said second annulus,forcing with a gas substantially all washing fluid from said secondannulusconductor means-conduit means assembly. and placing in saidsecond annulus cement with a controlled water content.

2. A method according to claim 1 wherein said washing fluid is liquidwater and said gas is air.

3. A method according to claim 1 wherein after placing cement in saidfirst, second, and third annuli, wash fluid is passed down said conduitmeans to break said rupture means. and cement and any other material insaid second annulus is washed out of that annulus to the earths surfaceby passing wash fluid (a) down said conduit means and up said secondannulus, (b) down said second annulus and up said conduit means. or (c)a combination of (a) and (b), and thereafter said wash fluid is forcedout of said second annulus by forcing a gas down said second annulus andup said conduit means.

4. A method according to claim 3 wherein said wash fluid is liquid waterand said gas is air.

1. A method for completing a well whose wellbore passes through apermafrost zone comprising, in at least a portion of said permafrostzone, placing in said wellbore a first casing means which carries nearthe lower end thereof a conductor means for passing fluid between theinside and outside of said first casing means, said conductor meansinitially having a rupture means for preventing the passage of fluidtherethrough, said first casing means being spaced from the wellborewall to provide a first annulus, conduit means extending in said firstannulus from said conductor means to the surface of the earth, placing asecond casing means inside said first casing means but spaced therefromto provide a second annulus between said first and second casing means,said second casing means extending below the lower end of said firstcasing means to provide a third annulus around that portion of saidsecond casing means which extends below said lower end of said firstcasing means, placing cement in said first, second and third annuli,before said cement hardens, breaking said rupture means, circulating awashing fluid through said second annulus-conductor means-conduit meansassembly to wash substantially all material out of said second annulus,forcing with a gas substantially all washing fluid from said secondannulus-conductor means-conduit means assembly, and placing in saidsecond annulus cement with a controlled water content.
 2. A methodaccording to claim 1 wherein said washing fluid is liquid water and saidgas is air.
 3. A method according to claim 1 wherein after placingcement in said first, second, and third annuli, wash fluid is passeddown said conduit means to break said rupture means, and cement and anyother material in said second annulus is washed out of that annulus tothe earth''s surface by passing wash fluid (a) down said conduit meansand up said second annulus, (b) down said second annulus and up saidconduit means, or (c) a combination of (a) and (b), and thereafter saidwash fluid is forced out of said second annulus by forcing a gas downsaid second annulus and up said conduit means.
 4. A method according toclaim 3 wherein said wash fluid is liquid water and said gas is air.